Polyester textile waste recycling

ABSTRACT

A method for recycling polyester from a polyester textile. The method comprises the steps of: providing said polyester textile soaked in a mixture comprising a solvent and a catalyst, providing and maintaining a temperature of said mixture comprising said polyester textile within a range of 80-240° C. during depolymerization of polyester in said polyester textile and wherein, in said step of providing said polyester textile soaked in said mixture, said catalyst of said mixture comprises calcium hydroxide. A catalyst may be used for depolymerization of polyester in a polyester textile, wherein the catalyst comprises calcium hydroxide. Natural fibers may be recovered from a textile comprising polyester and natural fibers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.17/268,238, filed Feb. 12, 2021, which is a national phase under 35U.S.C. § 371 of PCT International Application No. PCT/EP2019/072003which has an International filing date of Aug. 16, 2019, which claimspriority to European Application No. 18189517.8, filed Aug. 17, 2018,the entire contents of each of which are hereby incorporated byreference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for recycling polyestertextile and use of a catalyst for recycling polyester textile.

BACKGROUND OF THE INVENTION

Various of polyester polymers, such as polyalkylene terephthalates, arecommonly used in e.g. fibers due to for example their excellent chemicalstability, fibers which may be used for manufacturing polyestertextiles. Such textiles may be made from solely polyester fibers butthey may be made from a mixture of fibers. For example, polyestertextiles comprising both polyester and cotton fibers are common forclothes.

Large quantities of such polyester textiles are produced andconsequently there is a large amount of polyester textile waste whichneeds to be recycled and/or reused. An efficient recycling would make itpossible to successfully produce new polyester textile instead of usingraw material (i.e. crude oil) to the same extent as before. The demandfor recycled clothes is increasing due to our increasing awarenessregarding sustainability.

However, to develop a practical system of recycling polyester textilewaste is difficult. A big obstacle is impurities in textiles, suchimpurities may for example be dyes or other fibers such as cottonfibers. Mixing cotton and polyester fibers provides a textile having theadvantages of both the cotton and the polyester. In addition, thesefabrics have lower price than pure cotton fabrics. The most commoncotton/polyester textiles comprise 65% cotton and 35% polyester, buttextiles with 50% cotton and 50% polyester are also easy to find.Moreover, dyes are commonly used for giving the polyester textile itscolor. In order to achieve a good color fastness, a high amount of dyeis incorporated into polyester fibers. For example, deep blue polyesterfabric may contain pigments as much as 6 wt %.

Fibers from a polyester textile may directly be recovered, e.g.separated from other types of fibers in the textile, and subsequently beused for manufacturing a new polyester textile. A problem with reusingthe fibers like this is that the polyester chains have degraded, i.e.they become shorter, during usage of the polyester textile. Since thereused fibers comprise shorter polyester chains they will be of a poorerquality than fibers with longer polyester chains and therefore theresulting textile will also be of a poorer quality.

Alternatively, the polyester textiles may be chemically recycled. Thisincludes a depolymerization of the polyester in the textile. Thepolyester will then be depolymerized to its monomer, dimer and/or trimerunits which may subsequently be repolymerized to longer polyester chainswhich can be used for producing new fibers and hence new polyestertextile.

A problem with the current state-of-the-art is that the temperaturesused for the depolymerization of polyester are high in order to achievea high yield of the reaction. High temperature means that the energydemand for the depolymerization process is high, and thereby is also thecost of the process high. In addition, too high temperatures may beharmful for other types of fibers in the polyester textile, such ascotton fibers which may degrade during the depolymerization of thepolyester. It is desired to improve the current state-of-the-art inorder to lower the temperature of the depolymerization.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve the current state ofthe art and to mitigate the above mentioned problem. This and otherobjects are achieved by a method for recycling polyester from apolyester textile and by use of a catalyst for depolymerization ofpolyester in a polyester textile as described herein.

According to a first aspect of the invention a method for recyclingpolyester from a polyester textile is provided. The method comprises thesteps of:

-   -   providing said polyester textile soaked and/or immersed in a        heated mixture comprising a solvent and a catalyst wherein said        catalyst comprises calcium hydroxide;    -   maintaining said polyester textile in said heated mixture during        depolymerization of polyester in said polyester textile.

According to at least one example embodiment of the invention during thestep of maintaining said polyester textile in said heated mixture theheated mixture may have a temperature equal to or above thedepolymerization temperature of the polyester in the polyester textile.The depolymerization temperature being 80° C., or ° C., or 100° C., or110° C., or 120° C., or 140° C., or 160° C., or 180° C.

It shall be understood that the step of maintaining said textile in saidheated mixture comprises e.g. that the mixture heated to thedepolymerization temperature or a higher temperature and maintained atthis temperature during the depolymerization but also that the mixtureis heated to the depolymerization temperature and that the temperatureis thereafter lowered where after the temperature is raised to thedepolymerization temperature or above. This lowering and raising of thetemperature may be repeated one or more times.

According to a second aspect of the invention a method for recyclingpolyester from a polyester textile is provided. The method comprises thesteps of:

-   -   providing said polyester textile soaked and/or immersed in a        mixture comprising a solvent and a catalyst;    -   providing and maintaining a temperature of said mixture        comprising said polyester textile within a range of 80-240° C.        during depolymerization of polyester in said polyester textile;    -   wherein, in said step of providing said polyester textile soaked        and/or immersed in said mixture, said catalyst of said mixture        comprises calcium hydroxide.

This method provides a depolymerization of polyester at a lowertemperature as compared with the current state-of-the-art due to thecatalyst which is used in the method. Depolymerization at lowertemperatures facilitates for a more sustainable recycling of polyestertextiles, i.e. a more environmental friendly process, since the energydemand of the process may be decreased. Decreasing the required amountof energy may lead to a reduced cost for the recycling process. Thecatalyst used herein will depolymerize polyester to smaller molecules,e.g. to its monomers, dimers and trimers which may be referred to as thereaction products. These smaller molecules may after thedepolymerization be repolymerized to polyester which may be used toproduce a new polyester textile.

It shall be understood that the step of maintaining a temperature ofsaid mixture comprises e.g. that the mixture heated to said temperaturewhich may be referred to as the depolymerization temperature or a highertemperature but also that the mixture is heated to the depolymerizationtemperature and that the temperature is thereafter lowered below thedepolymerization temperature and thereafter raised again to thedepolymerization temperature or above. This lowering and raising of thetemperature may be repeated one or more times.

Embodiments mentioned below are compatible with both the first and thesecond aspect of the invention.

According to at least one example embodiment of the invention at least apart of the smaller molecules will be dissolved in the solvent. In otherwords, the monomers, dimers and trimers may partially be dissolved inthe solvent. This solution may be referred to as the liquid fraction.The catalyst and optionally any undepolymerized polyester and/or anyfurther solid material may be referred to as the solid fraction.

According to at least one example embodiment of the invention prior tothe step of providing the polyester textile soaked and/or immersed in amixture a large piece of polyester textiles may be divided to smallerpieces. The pieces may then be soaked and/or immersed in a mixturecontaining the solvent and the catalyst. By soaking it means that thepieces of textile are surrounded by the solvent and catalyst. Inrelation to this invention the term “providing the polyester textilesoaked in a mixture” means that the polyester textile is surroundedand/or immersed by the mixture. Thus, the term “providing the polyestertextile soaked in a (heated) mixture comprising a solvent and acatalyst” means that the polyester textile is surrounded and/or immersedand/or covered by said mixture so that said mixture/catalyst can act atleast on the surface of said textile and make it depolymerize. Accordingto one example, said textile is depolymerized layer by layer or surfaceportion by surface portion—i.e. when the top surface or top layer hasbeen depolymerized the mixture reaches a new surface portion (replacingthe previous surface portion) or the next layer, which is nowdepolymerized.

According to at least one example embodiment of the invention themixture comprising polyester textile 0.2-10 wt % catalyst, or 0.2-6 wt %catalyst, or 1-4 wt % catalyst. Additionally, or alternatively, themixture comprising the polyester textile comprises at least 0.2 wt %catalyst, or at least 1 wt % catalyst, or at least 2 wt % catalyst.Additionally, or alternatively, the mixture comprising the polyestertextile comprises at most 10 wt % catalyst, or at most 6 wt % catalyst,or at most 4 wt % catalyst, or at most 2 wt % catalyst. The amount ofcatalyst is calculated as compared with the amount of polyester in thepolyester textile. For example, using 2 wt % of catalyst results in that0.12 g catalyst is used if there is 6 g polyester in the polyestertextile.

According to at least one example embodiment the solvent may act as areactant in the depolymerization reaction. Additionally, oralternatively, the mixture may comprise an additional reactant neededfor the depolymerization reaction.

According to at least one example embodiment of the invention said stepof maintaining a temperature of said mixture comprising polyestertextile lasts until at least 20% of the polyester in said polyestertextile is depolymerized to molecules with a molecular weight lower than600 g/mol, or at least 50% of the polyester in said polyester textile isdepolymerized to molecules with a molecular weight lower than 600 g/mol,or at least 80% of the polyester in said polyester textile isdepolymerized to molecules with a molecular weight lower than 600 g/mol.

According to at least one example embodiment of the invention saidmethod further comprises the step of:

-   -   recovering of said molecules with a molecular weight lower than        600 g/mol.

According to at least one example embodiment of the invention therecovering may comprise one or several sub-steps. Examples of suchsub-steps are precipitation, filtration, extraction, soxhlet extraction,distillation. These sub-steps may be combined in various ways in orderto recover the molecules with a molecular weight lower than 600 g/mol.

According to at least one example embodiment of the invention thedepolymerization products may be e.g. monomer, dimers and trimers of thepolyester in the polyester textile.

According to at least one example embodiment of the invention, themaintaining of the temperature in the step of maintaining thetemperature of the mixture comprising polyester textile lasts until20-100% of the polyester in said polyester textile is degraded, or until35-80% of the polyester in said polyester textile is degraded, or until50-70% of the polyester in said polyester textile is degraded.Additionally, or alternatively the step of maintaining the temperatureof the mixture comprising polyester textile lasts until at least 20%, oruntil at least 30%, or until at least 40%, or until at least 50% of thepolyester in said polyester textile is degraded. Additionally, oralternatively the step of maintaining the temperature of the mixturecomprising polyester textile lasts until at most 99%, or at most 90%, orat most 80%, or at most 70%, or at most 60%, or at most at most 50% ofsaid polyester in said polyester textile is degraded.

The fraction of polyester in the polyester textile which has degradedmay be referred to as the degradation efficiency (E). This efficiencymay be calculated from the weight of the solid fraction. Since thecatalyst is not consumed during the reaction the weight of the catalystcomprised in the mixture from start is the same as the weight ofcatalyst in the solid fraction after depolymerization it may be removedfrom the total weight of the solid fraction in order to calculate theamount of undepolymerized polyester. The depolymerization efficiency (E)may then be calculated according to:

$E = \frac{{a{mount}{of}{polyester}{in}{the}{textile}} - {{the}{amount}{of}{{undepol}.{polyester}}}}{a{mount}{of}{polyester}{in}{the}{textile}}$

-   -   According to at least one example embodiment of the invention        said temperature or depolymerization temperature is within the        range of 80-170° C., or within the range of 100-150° C. The        lower temperature that is used, the lower is the amount of        energy needed for the reaction.

According to at least one example embodiment the temperature is in therange of 80-200° C., or it is in the range 80-180° C., or it is in therange 80-160° C., or it is in the range of 80-140° C., or in the rangeof 80-120° C., or in the range of 80-100° C. Additionally, oralternatively, the temperature may be above 80° C., or above 90° C., orabove 100° C., or above 110° C., or above 120° C., or above 140° C., orabove 160° C., or above 180° C. Additionally or alternatively, thetemperature may be lower than 200° C., or lower than 180° C., or lowerthan 160° C., or lower than 140° C., or lower than 120° C., or lowerthan 100° C.

According to at least one example embodiment of the invention the methodaccording to any one of the preceding claims, wherein, in said step ofmaintaining said temperature of said mixture comprising said polyestertextile, said temperature is maintained for 10-300 min, or for 30-240min, or for 60-120 min.

According to at least one example embodiment the temperature ismaintained for at least 10 min, or at least 20 min, or at least 30 min,or at least 40 min, or at least 50 min, or at least 60 min.Additionally, or alternatively the temperature is maintained for at most300 min, or at most 270 min, or at most 240 min, or at most 200 min, orat most 160 min, or at most 120 min, or at most 90 min, or at most 60min. For example, the temperature may be maintained for 20-160 min, orit may be maintained for 50-200 min.

According to at least one example embodiment of the invention saidsolvent comprises an alcohol or a diol. The alcohol may serve as areactant in the depolymerization reaction.

According to at least one example embodiment of the invention thesolvent may be a linear or a branched alcohol or diol.

According to at least one example embodiment of the invention thealcohol may be chosen from a list comprising but not limited to:methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol or anyother alcohol comprising a carbon chain with more than eight carbons. Analcohol comprising a short carbon chain is more reactive than an alcoholcomprising a longer carbon chain, i.e. methanol will be the mostreactive alcohol.

According to at least one example embodiment of the invention the diolmay be chosen from a list comprising but not limited to: ethyleneglycol, propandiol or butanediol or any other diol comprising a carbonchain with more than four carbons.

According to at least one example embodiment of the invention the saidmixture comprises solely one alcohol or diol as solvent. In such anembodiment the depolymerization reaction and product purifications mayoccur in a water-free environment.

According to at least one example embodiment of the invention thealcohol could have also other functional groups, such as an amino groupor a primary amine.

According to at least one example embodiment of the invention saidpolyester textile comprises at least 10% polyester, or at least 25%polyester, or at least 50% polyester, or at least 75% polyester orwherein said polyester textile comprises 100% polyester.

According to at least one example embodiment of the invention thepolyester textile comprises at least 10% polyester, or at least 25%polyester, or at least 35% polyester, or at least 50% of polyester, orat least 70% polyester, or at least 80% polyester, or at least 90%polyester. Additionally, or alternatively, the polyester textilecomprises at most 90% polyester, or at most 80% polyester, or at most70% polyester, or at most 50% polyester, or at most 30% polyester. Forexample, the polyester textile may comprise 25-70% polyester, or it maycomprise 35-80% polyester.

According to at least one example embodiment of the invention, saidpolyester textile further comprise natural fibers and/or additionalsynthetic fibers, wherein said natural fibers for example are e.g.cotton fibers, viscose fibers, cellulose fiber or regenerated cottonfibers and wherein said synthetic fibers for example are elastanefibers.

According to at least one example embodiment of the invention the methodas described herein may allow for recovering the natural fiber from thepolyester fabric. Maintaining the mixture comprising the polyestertextile at as low temperature as possible is advantageous as it does notdegrade the natural fiber, e.g. a cotton fiber, as much as it maydegrade at higher temperatures. Hence, cotton fibers with highermolecular weight distribution is preserved after the reaction. Suchcotton fibers having a higher molecular weight distribution is easier touse for regeneration of cotton fibers, e.g. to produce a new textile. Inaddition, the regenerated cotton fibers may be stronger and consequentlyany textile produced from these fibers may have a higher quality.According to at least one example embodiment of the invention theregenerated cotton fiber may for example be a lyocell type fiber.

According to at least one example embodiment of the invention thepolyester textile may comprise further comprise yet another material,e.g. elastane. Elastane may also be separated using the method asdescribed herein.

According to at least one example embodiment of the invention thenatural fiber and/or any other material comprised in the polyestertextile may be a part of the solid fraction achieved after thedepolymerization reaction. Hence, the weight of this material may alsobe substracted from the total weight of the solid fraction in order tocalculate the depolymerization efficiency as described above.

According to at least one example embodiment of the invention thepolyester textile may further comprises a dye, e.g. pigments or coloringagents. The dye may be recovered and reused in new textiles.

According to at least one example embodiment of the invention saidpolyester is aromatic polyester or an aliphatic polyester, e.g. apolyalkylene terephthalate; and wherein said depolymerized polyestercomprises at least one of dimethyl terephtalate, ethylene glycol,1,3-propanediol, 1,4-butanediol, ethyl methyl terephthalate, dimers ofthe aromatic polyester, and trimers of aromatic polyester.

According to at least one example embodiment the aromatic polyester maybe polyethylene terephthalate (PET), or it may be polytrimethyleneterephthalate (PTT), or it may be polybutylene terephthalate (PBT), orit may be an aliphatic polyester such as polylactic acid (PLA).

According to at least one example embodiment of the invention saidcatalyst further comprises an oxide of any metal from group 2 of theperiodic table, such as CaO, or an oxide of any metal from thelanthanides. An oxide comprising any metal from group 2 of the periodictable shows a strong alkalinity and hence these oxides enhance thecatalyzation of the depolymerization. An oxide comprising a metal fromthe lanthanides the will also enhance the catalyzation of thedepolymerization, and in addition such oxide may increase the life timeof the catalyst.

According to at least one example embodiment of the invention saidcatalyst is written on the general formula Ca(OH)₂-xO-yO, where x ischosen from group 2 of the periodic table and where y is chosen from thelanthanides.

According to at least one example embodiment the catalyst may beCa(OH)₂—MgO—CeO₂. The ratio may be 1:4:1, i.e. the catalyst used may be1Ca(OH)₂-4MgO-1CeO₂.

According to at least one example embodiment of the invention saiddepolymerization is performed in an autoclave.

According to at least one example embodiment of the invention thedepolymerization is performed in an autoclave, such as at 1-30 bar,preferably at 1-6 bar.

According to at least one example embodiment of the autoclave is filledwith an inert gas, e.g. nitrogen or argon, prior the depolymerization.The autoclave may be filled with such inert gas prior pressurizing theautoclave.

According to at least one example embodiment of the invention saidmethod further comprises the step of:

-   -   Recovering of said at least one of dimethyl terephtalate,        ethylene glycol, 1,3-propanediol, 1,4-butanediol, ethyl methyl        terephthalate, dimers of aromatic polyester, and trimers of an        aromatic polyester.

According to at least one example embodiment of the invention therecovering may comprise one or several sub-steps. Examples of suchsub-steps are precipitation, filtration, extraction, soxhlet extraction,distillation. These sub-steps may be combined in various ways in orderto recover at least one of dimethyl terephtalate, ethylene glycol,1,3-propanediol, 1,4-butanediol, ethyl methyl terephthalate, dimers ofaromatic polyester, and trimers of aromatic polyester.

According to at least one example embodiment of the invention themixture is cooled in order to let some of the reaction products e.g.dimethyl terephthalate, dimers and trimers to precipitate before thefiltration. By this precipitation these reaction products may become apart of the solid fraction.

According to at least one example embodiment of the invention themixture is first cooled allowing some of the reaction products toprecipitate. The liquid fraction may subsequently be separated from thesolid fraction via filtration. The recovering of at least one ofdimethyl terephtalate, ethylene glycol, 1,3-propanediol, 1,4-butanediol,ethyl methyl terephthalate, dimers of aromatic polyester, and trimers ofaromatic polyester may subsequently be done via extraction and/orsoxhlet extraction of the solid fraction using methanol. This will e.g.separate some of the monomers, dimers and trimers from each other aswell as from the catalyst.

Additionally, or alternatively, the ethylene glycol may be separatedfrom the solvent by distillation if the solvent is another alcohol ordiol than ethylene glycol. If ethylene glycol is used as the solvent ofreaction this step of the recovering is unnecessary.

According to at least one example embodiment of the invention the methodmay further comprise the step of recovering any component of thepolyester textile, e.g. dye, natural fibers, elastane fibers ordepolymerized elastane.

According to at least one example embodiment of the invention therecovering of at least one of dimethyl terephtalate, ethylene glycol,1,3-propanediol, 1,4-butanediol, ethyl methyl terephthalate, dimers ofaromatic polyester, and trimers of aromatic polyester and the recoveringof any component of the polyester textile may be done simultaneously.Hence, the same steps may be used for recovering of both.

According to at least one example embodiment of the invention therecovering of any component of the polyester textile may comprise one orseveral sub-steps. Examples of such sub-steps are precipitation,filtration, extraction, soxhlet extraction, distillation. Thesesub-steps may be combined in various ways in order to recover anycomponent of the polyester textile.

According to at least one example embodiment of the invention the dyemay be recovered by e.g. filtration and distillation or extraction anddistillation process. The dye may be fully or partially soluble in thesolvent which is used in the mixture in which the polyester textile issoaked. If so, the solid fraction, e.g. undepolymerized polymer andcatalyst, is removed by filtration and subsequently the dye may berecovered by removing the solvent by distillation. Additionally, oralternatively, the dye may be insoluble in the solvent. The dye wouldthen be a part of the solid fraction and collected by filtration. Asolvent in which the dye is soluble may then be used to separate the dyefrom the rest of the solid fraction.

According to a third aspect of the invention use of a catalyst fordepolymerization of polyester in a polyester textile is provided. Thecatalyst comprises calcium hydroxide.

Effects and features of this third aspect of the present invention aremost analogous to those described above in connection with the first andthe second aspect of the inventive concept. Embodiments and examplesmentioned in relation to the first and the second aspect of the presentinvention are largely compatible with the third aspect of the invention.

According to at least one example embodiment of the invention saidcatalyst further comprises an oxide of any metal from group 2 of theperiodic table, such as CaO, or an oxide of any metal from thelanthanides.

According to at least one example embodiment of the invention saidcatalyst is written on the general formula Ca(OH)₂-xO-yO, where x ischosen from group 2 of the periodic table and where y is chosen from thelanthanides.

According to at least one example embodiment the catalyst may beCa(OH)₂—MgO—CeO₂. The ratio may be 1:4:1, i.e. the catalyst used may be1Ca(OH)₂-4MgO-1CeO₂.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects, as well as additional objects, features andadvantages of the present invention, will be more fully appreciated byreference to the following illustrative and non-limiting detaileddescription of preferred embodiments of the present invention, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 shows a schematic view of the method in accordance with at leastone embodiment of the invention;

FIG. 2 shows a schematic view of the method in accordance with at leastone embodiment of the invention;

FIG. 3 shows photographs visualizing the different steps comprised inthe method in accordance with at least one embodiment of the invention;

FIG. 4 shows graphs of the molecular weight distribution of cottonbefore and after depolymerization of polyester.

DETAILED DESCRIPTION OF THE DRAWINGS

In the present detailed description, embodiments of the presentinvention will be discussed with the accompanying figures. It should benoted that this by no means limits the scope of the invention, which isalso applicable in other circumstances for instance with other types orvariants of methods for recycling polyester from a polyester textilethan the embodiments shown in the appended drawings. Further, thatspecific features are mentioned in connection to an embodiment of theinvention does not mean that those components cannot be used to anadvantage together with other embodiments of the invention.

FIG. 1 shows a schematic view of a method 1 for recycling polyester froma polyester textile. The method comprises two steps 2, 4. The first stepcomprising providing a polyester textile soaked in a mixture comprisinga solvent and a catalyst. The second step 4 comprises providing andmaintaining a temperature of the mixture within a range of 80-240° C.during depolymerization of polyester in the polyester textile. Forexample, the temperature which is provided and maintained may be 100°C., or 120° C., or 150° C., or 170° C. The temperature is according toat least one example embodiment maintained until at least 20% of thepolyester in the polyester textile is depolymerized to molecules with amolecular weight lower than 600 g/mol. In other embodiments thetemperature is maintained until at least 50% or at least 80% of thepolyester in said polyester textile is depolymerized to molecules with amolecular weight lower than 600 g/mol. The temperature may e.g. bemaintained for min.

The polyester textile may comprise at least 10%, or 25%, or 50% or 75%of polyester and it may further comprise a natural fiber, e.g. cotton,regenerated cotton or viscose. Alternatively, the polyester textile mayalso comprise 100% polyester fibers. The polyester may for example be anaromatic polyester, such as a polyalkylene terephthalate. Examples ofsuch polyalkylene terephthalate is polyethylene terephthalate,polytrimethyl terephthalate and polybutylene terephthalate. The catalystcomprises calcium hydroxide. It may for example be Ca(OH)₂, or it may beCa(OH)₂—CeO₂, or it may be Ca(OH)₂—MgO—CeO₂. In the latter case theration may be 1:4:1, i.e. the catalyst used may be 1Ca(OH)₂-4MgO-1CeO₂.The solvent may comprise an alcohol or a diol.

FIG. 2 shows a schematic view of a method 201. The two first steps 202,204 of the method 201 in FIG. 2 are the same as the two steps 2, 4 ofthe method 1 in FIG. 1 . Hence, focus on the description related to FIG.2 will be on the differences compared to the method 1 of FIG. 1 .

The method 201 has a third step 206, which comprises recovering of saidat least one of dimethyl terephthalate, ethylene glycol,1,3-propanediol, 1,4-butanediol, ethyl methyl terephthalate, dimers ofaromatic polyester, and trimers of aromatic polyester. The third step206 may also comprise recovering of any dye, any natural fiber e.g.cotton and/or any additional component e.g. elastane. This step may bedivided into one or several sub-steps. Examples of such sub-steps areprecipitation, filtration, extraction, soxhlet extraction, distillation.These sub-steps may be combined in various ways in order to recover anycomponent of the polyester textile. In addition, the third step maycomprise recovering of any natural fiber, any further material and/orany dye which may be present in the polyester textile.

FIG. 3 shows photographs visualizing the different steps of method 201.In this example embodiment the polyester textile 220 comprisespolyethylene terephthalate (PET) and a dye. During the depolymerizationthe polyethylene terephthalate will depolymerize into its monomers, i.e.dimethyl terephthalate and ethylene glycol as well as dimers and trimersof the polyester. The textile 220 is soaked in a mixture comprising asolvent and a catalyst. In other words, the polyester textile isprovided soaked in a mixture comprising a solvent and a catalyst 202.Subsequently, a temperature will be provided and maintained duringdepolymerization of polyester in the polyester textile 204. Afterdepolymerization the reaction mixture 222 contains a solid fraction 222a and a liquid fraction 222 b. The reaction mixture 222 willsubsequently go through the third step 206 of the method in order torecover reaction products, dye and solvent. This third step 206 isdivided into several sub-steps. After the reaction the reaction mixturemay be cooled for precipitating some of the reaction products, e.g.dimethyl terephthalate as well as dimers and trimers of the polyestersuch that they become a part of the solid fraction. Hence, afterprecipitation the solid fraction 222 a comprises the precipitatedreaction products, the catalyst and undepolymerized polyester ifpresent. The liquid fraction 222 b comprises the solvent, dye andethylene glycol. The liquid fraction 222 b will be separated from thesolid fraction via filtration. The solid fraction will undergoextraction or soxhlet extraction 206 b using methanol such that dimethylterephtalate 224 is recovered and separated from the remaining solidfraction. This liquid fraction 222 b comprises dye, ethylene glycol andmethanol and is subsequently or simultaneously distillated 206 c. Duringdistillation 206 c, ethylene glycol 230 is recovered and separated froma solution comprising methanol and dye. The methanol may be evaporated206 d in order to recover the dye 228.

FIG. 4 shows the molecular weight of cotton present in the polyestertextile before (solid line) and after depolymerization of polyester at165° C. (dotted line) and at 190° C. (dashed line). The graph shows thata lower temperature for depolymerization does not affect, i.e. lower,the molecular weight distribution of the cotton fraction of thepolyester textile as much as a higher temperature. Hence, it isfavorable to be able to keep the temperature which is maintained duringdepolymerization as low as possible.

The skilled person realizes that a number of modifications of theembodiments described herein are possible without departing from thescope of the invention, which is defined in the appended claims. Forinstance, textiles of different compositions or different polyesters maybe recycled using this method.

EXAMPLES

Several catalysts were tested at different temperatures in order to finda catalyst working at low temperature.

Table 1 indicates which catalyst that were working at the differenttemperatures. In table 1, x means that the catalyst does not work and √means that the catalyst work. It shall be understood, the by working itmeans that the catalyst will trigger the depolymerization of thepolyester in the polyester textile.

Low Medium High temperature temperature temperature Name <160° C.160-200° C. >200° C. Al₂O₃ x x x Fe₃O₄ x x x CaO ✓ ✓ ✓ Ca(OH)₂ ✓ ✓ ✓ MgOx x ✓ CeO₂ x x ✓ CaO—CeO₂ ✓ ✓ ✓ MgO—CeO₂ x x ✓ 1CaO⁻4MgO⁻1CeO₂ ✓ ✓ ✓4MgO—CeO₂—Fe₃O₄ x x ✓ 4MgO—PrO_(x)—CeO₂ x x ✓

From this first screening of temperatures the four catalysts: CaO,Ca(OH)₂, CaO—CeO₂ and CaO-4MgO-1CeO₂, which were working at low andmedium temperature were further tested (cf. Examples 1-14 below). Table3 shows results from these tests.

Example 1

A mixture of 6 g of polyethylene terephthalate (PET) fiber soaked of 60ml methanol and 0.12 g of CaO were put in an autoclave. The autoclavewas heated to and maintained at 80° C. during the depolymerization.After 14 h, the autoclave was quenched to room temperature by cold waterallowing precipitation of dimethyl terephthalate (DMT) as well as dimersand trimers of the polyester. The liquid fraction was separated from thesolid fraction by filtration. 3.11 g of DMT was extracted from the solidfraction by methanol. Methanol and ethylene glycol were recovered bydistillation of the liquid fraction.

Example 2

A mixture of 6 g of PET-fiber soaked 60 ml methanol and 0.12 g of aCaO—CeO₂ mixed oxide were put in an autoclave. The autoclave was heatedto and maintained at 100° C. during the depolymerization. After 4.5 h,the autoclave was quenched to room temperature by cold water allowingprecipitation of DMT as well as dimers and trimers of the polyester. Theliquid fraction was separated from the solid fraction by filtration.4.07 g of DMT was extracted from the solid fraction by methanol.Methanol and ethylene glycol were recovered by distillation of theliquid fraction.

Example 3

A mixture of 6 g of PET fiber soaked in 60 ml of methanol and 0.12 g ofa 1CaO-4MgO-1CeO₂ mixed oxide were put in an autoclave. The autoclavewas heated to and maintained at 135° C. After 4.5 h, the autoclave wasquenched to room temperature by cold water allowing precipitation of DMTas well as dimers and trimers of the polyester. The liquid fraction wasseparated from the solid fraction by filtration. 4.61 g of DMT wasextracted from the solid fraction by methanol. Methanol and ethyleneglycol were recovered by distillation of the liquid fraction.

Example 4

A mixture of 6 g of PET fiber soaked in 60 ml methanol and 0.12 g of a1CaO-4MgO-1CeO₂ mixed oxide were put in an autoclave. The autoclave washeated to and maintained at 165° C. during the depolymerization. After 2h, the autoclave was quenched to room temperature by cold water. Thereaction mixture was put in freezer for 1 h in order to furtherprecipitate DMT as well as dimers and trimers of the polyester. Theliquid fraction was separated from the solid fraction by filtration.5.31 g of DMT was extracted from the solid fraction by methanol. Themethanol and ethylene glycol was recovered by distillation.

Example 5

A mixture of 8 g of PET textile waste with different colors soaked in 60ml methanol and 0.12 g of a 1CaO-4MgO-1CeO₂ mixed oxide were put in anautoclave. The autoclave was heated to and maintained at 165° C. duringthe depolymerization. After 2 h, the autoclave was quenched to roomtemperature by cold water. The reaction mixture was put in freezer for 1h to further precipitate DMT as well as dimers and trimers of thepolyester. The liquid fraction was separated from the solid fraction byfiltration. DMT was extracted from the solid fraction by methanol. Theextracted DMT was further purified by distillation to generate a higherpurity. The liquid fraction comprising methanol, ethylene glycol and dyewas distilled.

Example 6

A mixture of 6 g of PET textile waste with one color soaked in 60 mlmethanol and of a 1CaO-4MgO-1CeO₂ mixed oxide were put in an autoclave.The autoclave was heated to and maintained at 165° C. during thedepolymerization. After 2 h, the autoclave was quenched to roomtemperature by cold water. The reaction mixture was put in freezer for 1h to further precipitate DMT as well as dimers and trimers of thepolyester. The liquid fraction was separated from the solid fraction byfiltration. DMT was extracted from the solid fraction by methanol. Theextracted DMT was further purified by recrystallization to generate ahigher purity. The liquid fraction comprising methanol, ethylene glycoland dye was distilled.

Example 7

10 g of white PET/cotton mixed textile waste with a weight ratio of 1:1(PET to cotton) soaked in 100 ml methanol and 0.2 g of a 1CaO-4MgO-1CeO₂mixed oxide were put in an autoclave. The autoclave was heated to andmaintained at 165° C. during the depolymerization. After 2 h, theautoclave was quenched to room temperature by cold water allowing forprecipitation of DMT as well as dimers and trimers of the polyester. Theliquid fraction was separated from the solid fraction by filtration.Here, the solid fraction mainly contains DMT and cotton. DMT wasextracted from solid fraction by methanol. The remaining cotton was thendried at 35° C. overnight. The dried cotton can be reused through awet-spinning process to produce regenerated cellulose fiber. Table 2shows the mechanical properties of regenerated cotton fiber made fromthe recovered cotton. The methanol and ethylene glycol in liquid phasewas recovered by distillation.

Table 2 shows mechanical properties of regenerated cotton fiber producedthrough a lyocell spinning process.

Dry Wet measurement measurement Titer, dtex 8.63 8.52 Tenacity, cN/dtex3.68 2.93

Example 8

A mixture of 4.8 g PET fiber mixed with 1.2 g spandex fiber soaked in 60ml methanol and 0.2 g of a 1CaO-4MgO-1CeO₂ mixed oxide were put in anautoclave. The autoclave was heated to and maintained at 165° C. duringthe depolymerization. After 2 h, the autoclave was quenched to roomtemperature by cold water allowing precipitation of DMT as well asdimers and trimers of the polyester. The liquid fraction was separatedfrom the solid fraction by filtration. Here, the solid fraction mainlycontains DMT and depolymerized spandex fraction which is not soluble inmethanol. DMT was extracted from the solid fraction by methanol and thenpurified by a distillation to generate higher purity. The liquidfraction comprising methanol, ethylene glycol and polyether fromdepolymerized spandex was separated by distillation.

Example 9

6 g of PET fiber, 30 ml of ethanolamine and 0.12 g of 1CaO.4MgO.1CeO₂mixed oxide were put in an autoclave. The autoclave was heat up to 115°C. and kept it at 115° C. during the depolymerization. After 2 h, theautoclave was quenched to room temperature by cold water. The reactionproducts in the reactor were mixed with 150 ml of hot deionised water.The obtained slurry from reactor was heated up to the boiling point andthen filtered immediately. The filtrate from filtration was kept in 4°C. overnight. During the storage time, the bis(2-hydroxyethyl)terephthalamide (BHETA) crystallized in the filtrate. The PET wascompletely depolymerized and around 5.6 g of BHETA was obtained.

Example 10

6 g of Polylactic acid (PLA) pellets, 60 ml of methanol and 0.12 g of1CaO.4MgO.1CeO₂ mixed oxide were put in an autoclave. The autoclave washeat up to 175° C. and kept it at 175° C. during the depolymerization.After 2 h, the autoclave was quenched to room temperature by cold water.The reaction mixture was separated by filtration. The PLA was completelydepolymerized. The filtrate from filtration was distilled to removemethanol. After distillation, 4.25 g of methyl lactate was obtained.

Example 11

6 g of Polytrimethylene terephthalate (PTT) fiber, 60 ml of methanol and0.12 g of 1CaO.4MgO.1CeO₂ mixed oxide were put in an autoclave. Theautoclave was heat up to 175° C. and kept it at 175° C. during thedepolymerization. After 2 h, the autoclave was quenched to roomtemperature by cold water. The reaction mixture was separated byfiltration. PTT was completely depolymerized and 2.6 g of DMT wasextracted from solid fraction by methanol. The liquid fraction wasdistilled and got methanol and 1,3-Propanediol. The obtained methanolwill be recycled.

Example 12

5 g of PET fiber, 50 ml of methanol and 0.1 g of Ca(OH)₂ were put in anautoclave. The autoclave was heated to 135° C. and kept at 135° C.during the depolymerization. After 4.5 h, the autoclave was quenched toroom temperature by cold water. A liquid fraction was separated from asolid fraction by filtration. 4.18 g of DMT was extracted from the solidfraction by methanol. Methanol and ethylene glycol were recovered bydistillation of the liquid fraction. The obtained methanol and ethyleneglycol may be recycled.

Example 13

5 g of PET fiber, 50 ml of methanol and 0.1 g of Ca(OH)₂ were put in anautoclave. The autoclave was heated to 165° C. and kept at 165° C.during the depolymerization. After 2 h, the autoclave was quenched toroom temperature by cold water. A liquid fraction was separated from asolid fraction by filtration. 4.09 g of DMT was extracted from the solidfraction by methanol. Methanol and ethylene glycol were recovered bydistillation of the liquid fraction. The obtained methanol and ethyleneglycol may be recycled.

Example 14

5 g of PET fiber, 50 ml of methanol and 0.1 g of Ca(OH)₂ were put in anautoclave. The autoclave was heated to 185° C. and kept at 185° C.during the depolymerization. After 1 h, the autoclave was quenched toroom temperature by cold water. A liquid fraction was separated from asolid fraction by filtration. 4.3 g of DMT was extracted from the solidfraction by methanol. Methanol and ethylene glycol were recovered bydistillation of the liquid fraction. The obtained methanol and ethyleneglycol may be recycled.

Table 3 shows the depolymerization efficiency and the yield of extractedDMT using different catalyst at different temperatures.

Reaction temperature 80° C. CaO CaO•CeO₂ Depolymerization 58.5% 43.6%efficiency Yield of Extracted 51.8% 18.7% DMT Reaction temperature 100°C. CaO•CeO₂ 1CaO•4MgO•1CeO₂ Depolymerization 83.5% 46.6% efficiencyYield of Extracted 67.8% 32.6% DMT CaO Ca(OH)₂ CaO•CeO₂ 1CaO•4MgO•1CeO₂Reaction temperature 135° C. Depolymeriza-  100%  100%  100%  100% tionefficiency Yield of 68.8% 83.6% 63.8% 76.8% Extracted DMT Reactiontemperature 165° C. Depolymeriza-  100%  100%  100%  100% tionefficiency Yield of 75.8% 81.8% 79.8% 88.5% Extracted DMT

1. A method for recovering natural fibers from a polyester textile,wherein said method comprises the steps of: providing said polyestertextile soaked in a mixture comprising a solvent and a catalyst;providing and maintaining a temperature of said mixture comprising saidpolyester textile within a range of 80-240° C. during depolymerizationof polyester in said polyester textile; and recovering natural fibersafter said depolymerization, wherein, in said step of providing saidpolyester textile soaked in said mixture, said catalyst of said mixturecomprises calcium hydroxide.
 2. The method according to claim 1, whereinsaid step of maintaining the temperature of said mixture comprising saidpolyester textile lasts until at least 20% of the polyester in saidpolyester textile is depolymerized to molecules with a molecular weightlower than 600 g/mol, or at least 50% of the polyester in said polyestertextile is depolymerized to molecules with a molecular weight lower than600 g/mol, or at least 80% of the polyester in said polyester textile isdepolymerized to molecules with a molecular weight lower than 600 g/mol.3. The method according to claim 1, wherein said natural fibers compriseat least one of cotton fibers, viscose fibers, cellulose fibers, andregenerated cotton fibers.
 4. The method according to claim 3, whereinsaid natural fibers comprise cotton fibers.
 5. The method according toclaim 1, wherein said temperature is within the range of 80-170° C., orwithin the range of 100-150° C.
 6. The method according to claim 1,wherein, in said step of maintaining said temperature of said mixturecomprising said polyester textile, said temperature is maintained for10-300 min, or for 30-240 min, or for 60-120 min.
 7. The methodaccording to claim 1, wherein said solvent comprises an alcohol or adiol.
 8. The method according to claim 1, wherein said polyester textilecomprises at least 10% polyester, or at least 25% polyester, or at least50% polyester, or at least 75% polyester, or said polyester textilecomprises 100% polyester.
 9. The method according to claim 1, wherein,after said depolymerization of polyester, reaction products of saiddepolymerization of polyester are separated from the natural fibers, thenatural fibers being present in a solid fraction.
 10. The methodaccording to claim 1, wherein said polyester textile further comprisesadditional synthetic fibers.
 11. The method according to claim 1,wherein said polyester is aromatic polyester, and wherein saiddepolymerized polyester comprises at least one of dimethyl terephtalate,ethylene glycol, 1,3-propanediol, 1,4-butanediol, ethyl methylterephthalate, dimers of the aromatic polyester, and trimers of thearomatic polyester.
 12. The method according to claim 1, wherein saidcatalyst further comprises an oxide of any periodic table group 2 metal,or an oxide of any lanthanide metal.
 13. The method according to claim1, wherein said catalyst has a general formula Ca(OH)₂-xO-yO, where x isany periodic table group 2 metal and where y is any lanthanide metal.14. The method according to claim 1, wherein said depolymerization isperformed in an autoclave.
 15. The method according to claim 11, whereinsaid method further comprises the step of: recovering said at least oneof dimethyl terephtalate, ethylene glycol, 1,3-propanediol,1,4-butanediol, ethyl methyl terephthalate, dimers of the aromaticpolyester, and trimers of the aromatic polyester.
 16. A methodcomprising using a catalyst for depolymerization of polyester in apolyester textile, wherein said catalyst includes calcium hydroxide. 17.The method according to claim 16, wherein said catalyst furthercomprises an oxide of any periodic table group 2 metal, or an oxide ofany lanthanide metal.
 18. The method according to claim 16, wherein saidcatalyst has a general formula Ca(OH)₂-xO-yO, where x is any periodictable group 2 metal and where y is any lanthanide metal.
 19. The methodaccording to claim 1, wherein said method further comprises the step of:producing new textile from the recovered natural fibers.
 20. A recoverednatural fiber obtainable based on depolymerization of polyester in atextile, the textile comprising the polyester and natural fibers, andrecovery of natural fibers after said depolymerization.
 21. The methodaccording to claim 17, wherein said catalyst further comprises CaO.